Drilling of a hard-to-cut material which is hard to machine is generally performed by an electrochemical machining method and an electro-discharge machining method. In particular, when a hard-to-cut material having a high aspect ratio is drilled, the electrochemical machining method is used (e.g., Patent Literature 1).
Meanwhile, when a long hole is machined in a workpiece by the electrochemical machining, there is a need to increase the current to increase the machining speed. Although the applied voltage is generally increased to increase the current, it is preferable to limit the applied voltage to a low level for safety reasons and from the viewpoint of saving energy.
In view of such circumstances, as a method for increasing the machining speed without increasing the applied voltage, using a method for increasing an electric conduction area of the electrode used in the electrochemical machining by increasing the thickness of the electrode can be considered. However, the thickness of the electrode is restricted by the machining hole diameter and the amount of the electrolyte supplied to the electrode. Therefore, it is difficult to simply change the thickness of the electrode to increase the electric conduction area. Here, since the outer circumferential surface of the electrode is coated with an insulating member, it is also possible to increase the electric conduction area by peeling off the coating.